1. Field of the Invention
The present invention relates to a link structure for connecting a plastic optical fiber, mainly used for high-speed communications, to a light receptor. The invention is also concerned with a light-relay element used in the link structure and a method of manufacturing the light-relay element.
2. Description of Background Information
A plastic optical fiber has a core portion, the diameter of which is usually greater than that of the other types of fiber such as a quartz-based optical fiber. This provides a benefit in that the plastic optical fiber can easily be connected to another piece of the same fiber, or to another kind of optical element. For this reason, the components used for the connection require no stringent accuracy. Such a plastic optical fiber provides an economical communications device, which can easily be aligned optically.
In the past when optical communications were mainly carried out at a relatively low speed, the common practice was to put the light-receiving face of a light receiver such as photo-diode unit, directly against the end face of the plastic optical fiber.
Recently, however, as the research into high speed optical communications using a plastic optical fiber has progressed, the connection between the fiber and a light receiver such as photo-diode unit began to create problems.
As is known, the response speed of a photo-diode unit is determined by the time in which the electrons, excited by the light entering into the light-receiving face of the light-receiving portion of the photo-diode unit, reach the electrode inside the photo-diode. In order to obtain a response speed applicable to high-speed optical communications exceeding several hundreds of Mbps, the light-receiving portion of the photo-diode unit must be miniaturized, so that the light-traveling time can be reduced.
Conversely, the miniaturized light-receiving portion can receive only a portion of the light emitted from the end face of plastic optical fiber, so that the connection loss between the fiber and the photo-diode unit is increased.